This application is a continuation of application Ser. No. 360,477, filed June 2, 1989, now abandoned.
The invention relates generally to trenching machines and, more specifically, to a trenching machine wherein the trench is advanced earliest at the bottom.
Conventional trenching machines employ, typically, a cutter bar which carries an endless cutter chain that is powered to travel around the cutter bar. A tractor unit carries the cutter bar which, in its operative position, extends downwardly and rearwardly relative to the direction of travel of the tractor unit. The cutter chain removes earth to create the trench generally along the forward and downward facing edge or face of the cutter bar. The chain travels in a direction to drag spoil fowardly and upwardly where appropriate means are used to divert it to the side of the trench.
Because the cutter chain of conventional trenching machines cuts into the earth along the forward and downward facing edge of the cutter bar, several disadvantages result. Spoil is dragged, rather than carried, to the surface along the face of the trench being cut. The reaction force exerted on the cutter chain is downward and rearward and so has a large component in the direction opposite to the tractive force being exerted by the tractor unit, which must, accordingly, expend additional energy to overcome this rearward force. Rocks and other aggregate material are forced forwardly and downwardly, making their release and transport to the surface more difficult. These same forces tend to compact the earth forwardly of the cutter bar, thereby making the trenching operation more difficult.
Conventional trenching machines also accumulate considerable spoil in the cutting area below the chain. Excess spoil passes around or through the chain and is conveyed upwardly toward the drive sprocket of the cutter bar where it may interfere with the driving of the sprocket and chain and may even wedge in to stop or break either structure. To the extent that the chain of conventional trenching machines acts as a conveyor, spoil carried by the chain may overrun the sprocket and be dumped back into the trench. Considerable force is often applied to the cutter bar to improve the cutting action of the chain, particularly when initiating the trench. This force reduces the stability of the tractor unit and can cause severe vibration in the machine and sideways tipping.